Format of ESDI POS Information Status Block:
Offset	Size	Description	)
 00h	BYTE	EAh
 01h	BYTE	number of words in block (05h)
 02h	WORD	magic value FFDDh
 04h	BYTE	POS register 3
 05h	BYTE	POS register 2
 06h	BYTE	POS register 5 (unused, FFh)
 07h	BYTE	POS register 4 (unused, FFh)
 08h	BYTE	POS register 7 (unused, FFh)
 09h	BYTE	POS register 6 (unused, FFh)